Filament structure for electrical discharge devices



June 10, 1947. J. w. SKEHAN 2,422,141

FILAMENT STRUCTURE FOR ELECTRICAL DISCHARGE DEVICES Filed May 19, 1945 2 Shets-Sheet 1 INVENTOR him ATTORNEY June 10, 1947. J. w. SKEHAN FILAMENT STRUCTURE FOR ELECTRICAL DISCHARGE DEVICES Filed May- 19, 1945 2 Sheets-Sheet 2 Patented June 10, 1947 'FILAMENT STRUCTURE. FOR ELECTRICAL- v DISCHARGE DEVICES Joseph W. Skehan, Stamford, Conn, assignor to Machlett Laboratorie s, Inc., Springdale; :111.,

a'corporation of Connecticut Application May 19, 1945, Serial No. 594,688

7 Claims. (Cl. 250-275) 1 "This invention relates to electrical discharge devices and is concerned more particularly with a novel cathode structure for use in such devices, which offers numerous advantages over prior structures, in that it is more rugged and simpler to manufacture. The new cathode structure may be advantageously employed in electron tubes of various kinds-but, since it is especially suited for-use in rectifier tubes, an adaptation of the invention for that use will be illustrated and described in detail for purposes of explanation. It will be apparent, however, that the utility of the invention is not limited to rectifier tubes and that the new'structure is of wider application.

The rectifier tube; in which the new cathode is to be used, has an anode of hollow cylindrical form into which the cathode'projects; The cathode ordinarily includes a plurality of filaments of' tungsten wire, for example, which are supported on rods-extending through one end wall of the tube and terminating within the anode.

The copending application of Skehan and Magnusson, Ser. No. 596,038, filed May 26, 1945, discloses a filament assembly, which may be advantag'eously used in a rectifier tube having a hollow cylindrical anode, and, in the construction of that application, each filament is anchored at each end to a pair of'fixed supports angularly offset by 180; for example, so that each filament is of generally'helical form. The filaments are of such shape and length, when cold; that, upon being heated, they expand to the desired final form, inwhich they are properly spaced from the'anode. The cathode structure of the present invention affords certain of the advantages of the structure of the copending application but differs therefrom in that the filaments are mounted in such manner that a less number of junctions of thefilaments to their supports is required. The supports-are also easier to make and, because of these; differences, it is easier to control the electrical characteristics of the present structure.

' For" a, better understanding of the invention, reference may be made to. the accompanying drawings, in which Fig. 1 is aview-in longitudinal section of a rec'- tifier tube provided with the cathode filament structure of the invention;

Fig. 2 is a sectional VieWOn the line. 2-2 of Fig. 1;

Fig. 3 is a view in side elevation'on an enlarged scale of the new filament structure shown in Fig.1;

Fig. 4 is a' viewisimilar to Fig. 3 but at right angles thereto and;

Fig. 5" is an end view of the structure shown in Fig. 3, looking from the left hand'end thereof.

Referring now to the drawings, the tube shown in Fig. 1' comprises a glass envelope I0 having an enlarged central portion Ina and necks lnb of reduced diameter having reeentrant ends l il'c, Hid. A- metal cup H is sealed to the end llic of one of the necks to close that end and a block I2 of suitable metal, such as steel, is mounted in the exposed bottom of thecup. A screw I3 is threaded into block l2 to contact with the cup II and a conductor M is connected to the screw and through it to the cup. A block l5 of suitable metal is mounted to enclose the end of cup l lwithin the tube and a cylindrical metal shield i6 is mounted on the block to enclose the seal between the rim of the cup and the envelope wall. A plurality of metal rods I1 extend through openings in block l5 and are connected at their outer ends to cup- II. Thecup I l, blocks l2 and I5, metal shield l6, and rods H are united, as by brazing, to form an integral assembly. The inner ends of rods I7 extend into one end of acylindrical anode |8-and are connected thereto: The anode lies coax-ially with the envelope and within the enlarged central portion [0a of the envelope.

A plurality of metal supporting rods lying in a plane and extending axially of the envelope are sealed through the closed end of the re-entrant' portion id of the envelope and therods are maintained in proper spaced relation by ablock l9 of insulation, through openings in which the rods extend. The outer tworods 20, 2| terminate just within the end of the anode near end Hid of the envelope, while-the remaining three rods 22, 23', 24 extend through the anode nearly to the opposite end thereof. The short rods 20, 2| and the centrallong rod 23 are for filament supporting purposes, while rods 22 and 24-serve both as filament supports and as conductors. The outer ends of rods Hand 24 are, accordingly, connectedto conductors 25a, 25b by which the filaments of the cathode are supplied with heating current and maintainedat'the proper potential'difierence relative to the anode. Rod23 carries a sleeve 26' to which is attached a' cup 21 shielding the seals of the rods through the envelope wall.

A metal strap 28, preferably of sheet'molybdenum, is: mounted on the'end'of each of'rods 22; 24 and extends outward therefrom, the-twostrapsj being aligned? ram strap is formed at one end witha loop 2811, which is fittedaround the end Of'fif rod, 22, 24" and welded thereto, and,

at its 'otherend, the strap is formed with a smaller loop 2817.; The. central rod 23 carries at it's 'free end a cross-piece in theform of a double strap 29 made of two strips of sheet molybdenum riveted face to face and formed with a central opening 29a for reception of the end of rod 23. The double strap is welded to the end of rod 23 and at its outer ends, the strap is formed with loops 2%. strap 29 extends at right angles to strap to the respective supports of the pair andjan chored between its ends 28 and loops 28b and 2917 are spaced equal distances from the axis of rod 23.

A sleeve 30 is mounted on the free end of each of rods 20, 2| and welded thereto. Each sleeve 30 is provided Withan integral strap 30a extending outwardly from the axis oi the rod on WhlCh to the third support.

2. In a cathode filament structure, the 'combination of a pair of fixed supports laterally spaced from and angularly spaced about the axis of the structure, a third support spaced longitudinally of. the structure from the pair of supports and lying spaced angularly about said axis from said "supports and at the same side of both saidsupports, a loop attached to the third support, and

a filament attached'rigidly at its ends to respectivesupports of the pair and passing through the it is mounted, and each strap; 30a terminates in a loop 307) lying in axial alignment with a loop 281) onastrap 28.' r V A filament 3| of tungsten wire, for example, has one end received in and welded tothe loop 281) of one of the straps 28 and the filament passes through the loop 3% on the strap 38a of one of the sleeves 3B. The filament then extends to the adjacent end of the double strap 29 and its'end is received in and welded to the loop 2329 on strap .29. A second filament is similarly connected atits ends to theloop 2% on the other strap '28 and to the loop 2% at'the other end of the double-strap 29. Between'its ends, the second filament passes through the loop 301) on the strap 30a of the other sleeve 39. With this arrangement, the ends of each filament are angularly offset 90, while its gularly by 90 from one by 180 fromthe other. The ends of the filament are welded to the end of one strap 28 and to one end of the double strap 29 and only two welds are required for -each filament. It is, therefore, relatively easy to maintain close control over the pointsof electrical contact of the filaments to the straps and thus avoid variations in the electricalcharacteristics of thefilaments mid-portionis offset an- In; the filament structure described, current supplied through conductor 25a, for example, flows through rodzd to the strap 28 mounted.

thereon, and thence through the filament 3! attached to the end of thestrap to one end of strap beformed, in accordance with the disclosure of the copending application of Skehan and Magnusson above identified, so that, when, in the cold condition, they lie-inward from thepositions that it is desired that they may occupy when they are heated and expanded. The positions of the hot expanded filaments, relative to the'anode, may thus be controlled, so that most satisfactory operation of the tube maybe obtained. I claim:

end of the filament and 1. In a cathode filament structure, the combi-r nation of a pair of fixed supports laterally spaced from and angularly spaced about the axis of the structure, a third support spaced'longitudinally f of the structure from the pair ofsupports and lying spacedangularly, about saidaxis from said supports and. at the same side of both said supports, and a filament attached rigidly at'its ends loop on the third support. r

'3, In a cathode filament structure, the combination of a pair of fixed supports laterally spaced from and angularly spaced about the axis of the structure, a third support spaced longitudinally of the structure from the pair of supports and lying spaced ang'ularly about said axis from said supports and at the same side of both saidv supports, anda filament attached rigidly at its ends to respective supports of the pair and having a portion between its ends secured to the r thirdsupport, the parts of the filamentbetween the third support and each support of the pair beingof generally helical form.

4. In a cathode filament structure the com bination of a pair of fixed supports laterally spaced from and angularly spaced about the-axis 0f the structure, a third support spacedlongi-e tudinally or the structure from the pair of sup-f ports, and a filament attached'rigidly at its ends to the respective supports of the pair and secured between its ends directly to the third support, th third support being angularly oilset about the axis of the structure from the pair, of sup.-

ports and lying at'thei same side of both-supports the portions of the filament between the third support and those of the pair being of un equal length.

5. In a cathode filament structure, the team nation of an even number'of supports arranged" in a. series about a central axis, half as many other supports spaced along the axis from the se- 'ries'of supports and disposed about saidaxis, a plurality of filaments, each rigidly attached at its ends to adjacent supports in the series 'andbe-i I tween its ends to one of said other supports which is'spaced angularly about theaxis from said adjacent supports and lies at the same side of both said. supports. Q I Y 6. .In a cathode filament structure, thecom-J bination of four supports arranged in a series about a central axis, two alternatesupports in the V series being electrically connected, a pair of supports spaced along the axis from the. series of supports and lying on opposite sides of said axis,

and a pair of filaments each connected rigidly. at, one end to a, pair of adjacent supports in the se-' ries and between its endsto a supporter the pair which lies ,ofiset' about the axis at the same side J which the endsjo f of said adjacent supports to the filament are secured;

'7. In a cathode filament structure, a groupoi five rods lying side by side in spaced relation in a plane, the two outer rods being shorterthan the thre inner ones, als'trap attached to eachshort rod and terminating in a loop offset. out- Wardly from the axis of therod inisaid plane,

"a member mounted on the end of eachouter long rod andfextending outwardly therefrom in said plane, each member terminating in"a"sleeve 1 aligned withone of said loops, at cross-pieceat-T tached to the en'd'of the central long rodan'd extending at right angles to said plane, said cross} 7 piece having terminal sleeves lying in a circle passing through the sleeves on said members, and a pair of filaments, each having one end secured in the sleeve on one member and its other end secured in the sleeve at; one end of the crosspiece, the filament passing through a loop on the short rod at the opposite side of the group from the long rod carrying the member in the sleeve of which one end of the filament is received.

- JOSEPH W. SKEHAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,334,716 Litton Nov. 23, 1943 1,980,804 Koch Nov. 13, 1934 10 1,916,446 Sutherlin July 1, 1933 1,745,181 Mischler Jan. 28, 1930 

